Solvent refining of oil



June 6, 1939. w.r P. GEE 4x-:T Al.

SOLVBNT REFINING OF OIL Filed March 27, 1937 Il mmJOOU INV TORS BY ff/l W WILLIAM P. G EE MAX NEuHAus X ATTORN EY Patented June 6,

vUNITED STATI-:sl

PATENT OFFICEl haus, Fishkill assignors to The Texas Company, New York, N. Y., a corporation of Delaware Application March 27, 1937, Serial No. 133,304

3 claims.

(Cl. 196-I3) 'I'his invention relates to a method of solvent perature. -A higher yield 'of separated oil is thus reiining hydrocarbon oil and has` particular reference to the refining of mineral lubricating oil. -The invention contemplates the solvent extrac- 5 tion of oil with a selective solvent, such as furfural, to produce a primary railinate phase con,- taining relatively high viscosity index oil, and a primary extract phase containing oil comprising constituents of low and intermediate viscosity are separated and the solvent removed therefrom. The extract phase, after a large portion, or substantially all, of the solvent is removed is sub- Jected to further extraction in a secondary extraction zone with a smaller proportion of the selective solvent in order to separate it into secondary extract and railnate phases. The seconde ary railinate phase contains oil of intermediate tains oil of relatively low viscosity index.`

A desirable method of proceeding in accordance with the invention involves .cooling the primary extract phase after its removal from the primary extraction zone to a temperature below that .prevailing inthe primary extraction zone so as to separate .therefrom an insoluble oil layer. The

solvent is, then stripped from the remaining solvent layer, all or in part, leaving a. heavyV extract.' The vinsoluble oil layer is subjected to countercurrent extraction in the secondary extraction parainic constituents which might votherwise be retained in the primary extract phase, as removed from the primary extraction zone.

A further modiiication of the process involves incorporating a portion of this heavy extract phase, from which the solventvhas been stripped, in the primary extraction'phase, after the removal of the latter from the primary extraction tower, and prior to subjecting the primary extract 55 .phase to settling. 'Y

'The heavy extract material thus incorporated ,in theprimary extract phase exerts a saltingout" effect such that a greater'proportion of oil of intermediate character is separated as anVin- 00 soluble fraction uponstanding at reduced temindex.l The primary extract and rainate phases character, while the secondary extract phase conzone with a portion of the solvent removed from Y the primary extract phase. .The heavy extractv obtained than when the primary extract phase is subjected merely to cooling and settling in the absence of the added heavy'extract material.

While furfural has been mentioned, it is contemplated that other solvents, having selective action as between constituents of the oil of. diiering viscosity indices, may be used as, for example, nitrobenzene, benzaldehyde, aniline, etc. 'I'he selective solvent may be used alone, or in the presas, for example, benzol and its homologs; ,light petroleum hydrocarbons, such as propane, gasoline or'naphtha; and other solvents, such as lowboiling aliphatic ethers. i

- The invention contemplates producingin the primary extraction a fraction of oil of relatively high viscosity index, preferably having a viscosity index of around 100; and in the secondary extraction the production of a substantial amount of oil of intermediate character having a viscosity index', for example, of around- 75.

The remaining oil contained-in the secondary extraction phase is of relatively low viscosity inA dex. Itmay, after removal of the solvent, be used as an inferior grade of lubricating oil, or may be disposed of in other ways, such as cracking stock for the production of motoriuel.

In order to facilitate description of the process of this invention, reference will now be' made to the accompanying drawing.

As shown in the drawing, the charge oil, comprising a lubricating oil stock, is obtained from a source not'shown and introduced vto the midportion of a primary extraction tower'l. The selective solvent obtained from a source not shown is also introduced tothe upper portion of this extraction tower. The'oil and solvent flow countercurrently to each other through the upper portion of the tower. Complete mixing and contact between the oil and solvent may be facilitated by suitable packing material provided Within the tower. Whereiurfural is used as the selective solvent, it is advantageous to maintain a relatively high temperature within the extraction tower. The temperature at the top of the tower may be as high as 300 F., while that at the bottom of the tower may be as high as 200 F. It isl desirable to maintain a temperature differential' -of around 60 or'more throughout the' extraction` z'one.

These temperature conditions maybe maintained by heating both 4the solvent and thev 01.1 to the necessary temperatures prior to introduction to the tower. j

The solvent is introduced to the tower advantageously in the proportion of about five, and in some instances as much as eight, parts oi solvent to one part of charge oil, where it is desired to l0 ence of a suitable auxiliary or modifying solvent produce a primary raffinate 'of quite high viscosity index oil.

t y Asa result of the contact between solvent and oil within the tower, primary extract and rafllnatephases are produced'. The ramnate phase, where furfural is the selective solvent, accumulates inl to 160 F. The cooled material is then introduced l to a separator 3 wherein separation into fractions or layers occurs. The upper layer comprises A"an oil of intermediatecharacter insoluble in the solvent, while the bottom layer comprises heavy extract oil dissolved -in a large body of solvent.

The heavy extract layer is Withdrawn from the bottom of the separator 3, and conducted to a stripper 4, wherein all or the major portion of the solvent is stripped and removed from the heavy extract. The solvent is removed as a vapor and condensed in a condenser 5. A portion of the condensed solvent is returned to the upper portion of the secondary extraction tower 6, while that portion not so returned may be conducted to tankage for further use in the primary extractor The insoluble oil accumulating in the upper.

-part of the separator 3 is withdrawn and introduced to the midi-portion of the extractor 8. It is here brought into countercurrent contact with the solvent liquid being introduced to the top of the secondary extractor.

-A portion of the heavy' extract from solvent has been stripped in the stripper 4 is introduced to the lower portion of the secondary extractor 6. In this way, the Solvent-oil, mixture accumulating in the lower portion of the extractor 6 is enriched with heavy extract which results in displacing a substantial amount of the more parafnic constituents retained inthe solvent-oil mixture descending in the extractor 6. 'I'he paraffim'c constituents so displaced are thus caused to accumulate in the upper portion of the extractor and are removed as a component of the secondary raillnate phase.

The secondary extract phase withdrawn from the bottom of the extractor 6 will thus comprise oil of relatively lowgviscosity index.

A portion of the heavy extract from which the solvent has beenstripped inthe stripper 4 is advantageously mixed with the primary extract` phase prior to introduction to the cooler 2, for the purpose of aiding and increasing the amount of oil separated in the separator 3.

If desired, some f the kheavy extract material may bel returned tothe bottom of the primaryk extraction tower, asiindicat'ed, for the purpose of favorably affecting the distribution of high'and low viscosity index constituents of the oil between the phases formed therein.

In some cases, it may be desired to'omit the -step of subjecting the primary extract phase to cooling and, settling. In that case, the primary extract phase is conducted through the connection- 1 directly to the stripper 4 wherein' substantially all the solvent is'removed. All the stripped extractvphase is then introduced to the lower portion of the extractor i, as indicted, and there subjected -to countercurrent extraction with a which the.

. have a viscosity index of around 75.

The following data are indicative of the results obtained by extracting. lubricating oil stock of Y mixed-base'ori'gin in the manner described above,

and `using the temperatures and solvent proportions speclfied..

The lubricating oil stock in question was subjected to countercurrent extraction with furfural in the primary extraction stage. 'I'he solvent was removed from the resulting primary ramnate phase, and the oil then dewaxed to produce a. dewaxed primary railnate oil amounting to about 44.8% by volume of the charge. The comparative laboratory tests on the charge and raflinate oil', before and after dewaxing, were as follows:

Primary ragiate Dewaxed r primary Charge removal rainate ofthe oil solvent 24. 0 31. 30. :I 1cm 515 cca B 72.13

4 115 115 0 0.92 0. 03 0. 02 Viscosity index 66 105 99 Vis. grav. cons 0. 838 0. 788 0. 792

The solvent was removed from the primary extract phase, and the extract oil remaining subjected to extraction with a smaller proportion of furfural at lower temperatures, as previously 'described, to produce'second'ary ramnate and 'extract phases. The solvent was removed from these phases. Secondary raffinate oil was dewaxed to produce-a dewaxedk oil amounting to about 25.2% by volume of the original charge.

The comparative tests on the primary extract,

4the secondary extract, and the secondary rafr iinate, before and after dewaxing, and-with the solvent removed, were as follows:

- Dewaxed Primary s'sfy Segd secondmt extract raiiinate gte l Gravity A. P. I 16.5 9.0 26. 5

S. U. Viscosityt W F 5250 850 1089 At 210 F 151 306. 4 l 73. 9 82. 7 Color tag rob Black Black 3% 2% PMU-.F 115 1 Percent carbon residue. f 3. 3 0. 13 Viscosity index. 21 74. 5 73 Vis. grav. con: 0, 888 Y 0. 043 0, 822

As a result of the foregoing extraction,A a yield of 4.8% ofprimary raffinate. having a viscosity index ot 99 after dewaxing, was obtained on the basis of the raw stock charged to the primary extraction tower. y A yield of 25.2% of secondary raiilnate oil, having a viscosity index of 73 after dewaxing, Awas obtained on the basis of the raw distillate charged tothe primary extraction tower. The combined yieldo f ramnate, oil was, '75

2,161,507 therefore, around '10% er the raw wax distillate` charge.

It is recognized that heretofore it has been proposed to extract in stages in which the phases from the primary stage have been subjected to Vcooling and settling, 'and the resulting separated vent has been stripped from it in a secondary extraction zone with a relatively smaller proportion of the same solvent under the samel or somewhat diierent temperature conditions.

The present invention involves using a relatively large proportion of selective solvent in the primary extraction step so as to produce a lubricating oil fraction of very high viscosity index, namely, around 100. The resulting extract phase, therefore, contains a large proportion of solvent which is advantageously removed, in whole or@ major part, so that the entire extract can be efiiciently treated in the second operation with a Vcontrolled smaller quantity of solvent applied countercurrently to produce a larger yield of the intermediate grade of oil.

The present invention, therefore, comprises a process adapted to produce, by solvent extraction methods, a lubricating oil of very high viscosity index as well as a high yield of oil of intermediate character having .a higher viscosity the charge.

It is, of course, contemplated that the solvent dosages and the extraction temperatures may vary from. those set forth in the above described specific examples dependent upon the nature of the oil being treated and the degree of extraction desired. A i

Obviously, many modications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims..

We claim: l 1. The method of solvent rening hydrocarbon oil which comprises extracting the oil with a relatively large proportion of a selective solvent at an elevated temperature of around 200 to 300 Fi, forming a` primary railinate phaseconsisting essentially of oil having a highI viscosity index of around and a primary extract phase comprising oil of low and intermediate viscosity index indexv than -dissolved in the bulk of the solvent, removing said primary phases, reducing the primary extract phase after removal from the primary stage to facilitate its separation into fractions, subjecting the insoluble oil fraction to countercurrent extraction with a further quantity of selective solvent, in relatively smaller proportion than that used in the primary stage in a secondary extraction zone in the absence of feed oil, maintaining said secondary extraction zone at a temperature of around 140 to 250 F., introducing a portion of the stripped heavy extract fraction to the secondary extraction zone, forming secondary extract and` rainate phases, and removing said phases.

2. The method of solvent rening mixed base mineral lubricating oil which comprises introducing the oil to the mid-portion of a primary extraction tower, introducing furfural to the upper portion thereof in relatively large proportion, maintaining the tower at a temperature of around 200 to 300 F., forming a primary railinate phase consisting essentially ofconstituents having a high viscosity index of around 100 and a primary extract phase comprising oil of low and intermediate viscosity index dissolved in the bulk o'f 'the solvent, removing said phases, reducing the temperature of the primary extract phase to around to 160 F.- to separate it into an insoluble'oil fraction and a heavy extract fraction containing the bulk of the solvent, stripping substantially'all of the solvent from the heavy extract fraction, introducing the insoluble oil fraction to the mid-portion of a secondary extraction tower wherein it is extracted in the absence of feed oil, introducing furfural to the upper portion of said secondary tower in relatively smaller proportion than that used in the primary stage. maintaining the tower at a temperature of around to 250 F., introducing a portion of ondary ramnate comprising oil of intermediate viscosity index and a'secondary extract phase rich in low viscosity index constituents, and removing said phases.

3. The method according to claim 2 in which a portion of the stripped heavy extract is incox'-,`

poratedintheprimaryextractphaseaiter removalfromthe primary stage toiacilitate itsv separation into fractions.

' WILLIAM P. GEE. 

